The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
Not applicable.
(1) Field of the Invention
The present invention generally relates to a sonar tracking array, and more particularly to a sonar tracking array for an active sonar system.
(2) Description of the Prior Art
Highly accurate sonar systems are continuously needed in today""s military and oceanographic environments. However, many conventional active sonar systems that operate at relatively high frequencies utilize an extremely large amount of components. Conventional high-channel count arrays, even if sparsely populated, contain a very high number of elements that significantly increase costs related to manufacturing, installation, maintenance and repair. Conventional short baseline tracking systems are unable to achieve adequate signal-to-noise ratio without the use of transponders and responders. The bearing measurement accuracy achievable with a sonar array is dependent on both the physical aperture of the array and the signal-to-noise ratio (SNR). The extent of the aperture available for mounting sonar arrays on submarines is limited. Thus, alternatively, narrow sonar beam-widths and correspondingly high angular resolution with a given fixed aperture can be achieved by operating at shorter wavelengths. However, high frequency (short wavelength) operation has a severe drawback in that sound propagation loss increases dramatically as described by R. J. Urick in xe2x80x9cPrinciples of Underwater Soundxe2x80x9d, McGraw Hill, New York, 1975, pages 99-102, which portion of a publication is incorporated herein in its entirety.
Receiver beamwidth is an expression of the angular sector within which the sonar tracking array responds to incident sounds. Outside the aforesaid angular sector, the response is severely attenuated. The 3 dB beamwidth of an array of sensors for a given uniformly shaded fixed aperture L is approximately represented by the equation 50 xcex/L wherein xcex is the wavelength in the transmission medium of the acoustic energy being generated. This concept is described by William S. Burdic in xe2x80x9cUnderwater Acoustic Systems Analysisxe2x80x9d, Prentice-Hall, Englewood Cliffs, N.J., 1991, page 310, which portion of a publication is incorporated herein in its entirety. If the array elements are spaced one-half wavelength apart, the number of elements across the aperture is then represented by the equation 2 L/xcex. Thus, for a square array, the channel count is proportional to L2.
What is needed is an improved sonar tracking array that is highly accurate but yet, is relatively less complex than conventional sonar tracking arrays. Another desirable feature of such an improved sonar tracking array is that it should have a relatively low per-unit-cost than conventional sonar tracking arrays.
It is therefore an object of the present invention to provide a sonar tracking array that is highly accurate but yet, is relatively less complex than conventional sonar tracking arrays.
Another object of the present invention is to provide a sonar tracking system that can operate at higher frequencies with relatively fewer hydrophone channels and yet achieve sufficient directivity.
A further object of the present invention is to provide a sonar tracking array that has a relatively lower per-unit-cost than conventional sonar tracking arrays.
The present invention is directed to a sonar array that is suitable for mounting to the exterior of a submarine. The sonar array exhibits relatively high accuracy but has a relatively low component and channel count. In a preferred embodiment, the sonar array is mechanically course steered in order to maintain the target within the main lobe response of the sonar array.
The sonar array of the present invention comprises a support structure, an acoustic projector attached to the support structure, and a plurality of directional hydrophones attached to the support structure and arranged so as to surround the acoustic projector. The directional hydrophones are spaced about the acoustic projector. In one embodiment, the array includes means attached to the support structure that allows the support structure to be connected to a device that effects course steering of the sonar array.
The sonar array of the present invention comprises a support structure, an acoustic projector attached to the support structure, and a plurality of directional hydrophones attached to the support structure and arranged so as to surround the acoustic projector. The directional hydrophones are spaced about the acoustic projector. In one embodiment, the array includes means attached to the support structure that allows the support structure to be connected to a device that effects coarse steering of the sonar array.
In one embodiment, all of the hydrophones are center-spaced from the acoustic projector by substantially the same distance.
In one embodiment, the plurality of hydrophones comprises four hydrophones.
In one embodiment, the outer diameter of the acoustic projector and each hydrophone is about 6.0 inches.
In one embodiment, each pair of successive hydrophones are center-spaced from each other by about 8.5 inches.
In a related aspect, the present invention is directed to a sonar tracking system, comprising a sonar array comprising a support structure, an acoustic projector attached to the support structure, and four directional hydrophones attached to the support structure and arranged so as to surround the acoustic projector. The directional hydrophones are spaced about the acoustic projector. The sonar tracking system further includes a mechanical turret for steering the sonar array. The turret has inputs for receiving control signals that control the movement of the turret. The sonar tracking array further includes means for receiving and processing sonar signals received from the hydrophones, and means, responsive to the processed acoustic signals, for generating the control signals for input into the mechanical turret.